class MyMath:
    # 加
    def add(self, a, b):
        return a + b

    # 减
    def sub(self, a, b):
        return a - b

    # 乘
    def mul(self, a, b):
        return a * b

    # 除
    def divi(self, a, b):
        return a / b

    # 幂
    def po(self, a, b):
        return a ** b

    # 开方
    def st(self, a, b):
        return a ** (1 / b)


a = MyMath()
x = 27
y = 3
print(f"x+y={a.add(x, y)}")
print(f"x-y={a.sub(x, y)}")
print(f"x×y={a.mul(x, y)}")
print(f"x÷y={a.divi(x, y)}")
print(f"x的y次方={a.po(x, y)}")
print(f"x的开y次方={a.st(x, y)}")


class Taxi:
    number = None

    def __init__(self, name):
        self.name = name


class Didi(Taxi):
    number = None
    def __init__(self, name="滴滴出行"):
        self.name = name


class Uber(Taxi):
    number = None
    def __init__(self, name="Uber优步中国"):
        self.name = name


b = Didi()
c = Uber()
print(f"hail {b.name}")
print(f"hail {c.name}")
